1. Field of the Invention
The present invention relates to a transmission apparatus for a bicycle, and more particularly to a transmission applying an endless transmission belt over a driving, rotating member and a multi-stage driven rotating member arranged at an output shaft that is cooperatively engaged with and rotated with a driving wheel of the bicycle.
2. Description of the Background Art
Applicants have determined that the background art suffers from the following disadvantages. Specifically, some bicycles have an output shaft that is always engaged with the driving wheel and provided with a one-way clutch in such a way that the bicycle can run even in the case that a driver stops pedaling, e.g., while operating the bicycle on a down-slope and the crankshaft is not rotated in a normal rotating direction.
In the case of the bicycle described in Patent Document Japanese Patent Laid-Open No. Hei (1997)-89012, a chain is wound around a large gear of a gear crank and a plurality of small gears installed at a rear hub, and a free wheel is installed at the rear hub. The free wheel is provided with an outer cylinder having said small gears connected in a relative unrotatable manner, an inner cylinder arranged inside the outer cylinder in such a way that is may be relatively rotated and connected to a hub member of the rear hub in such a way that it may not be relatively rotated, and a one-way clutch is arranged between the outer cylinder and the inner cylinder.
The one-way clutch transmits a driving power from the gear crank transmitted to the small gears only in one rotational direction from the outer cylinder to the inner cylinder. Therefore, when the pedals are driven in a forward direction, the driving power is transmitted to the outer cylinder of the free wheel through a chain and the small gears, and is further transmitted to the hub member through the one-way clutch and the inner cylinder to cause the rear wheel to rotate. In addition, when the large gear is not rotated, e.g., while operating on a down-slope or the like, the inner cylinder is always cooperatively engaged with the rear wheel through the one-way clutch but merely rotates in an idling state. The outer cylinder and the small gears are not rotated, and the chain therefore does not run.
The present inventors have determined that there is a need in the background art to improve the running performance of the bicycle due to the fact that the chain does not run when the bicycle is operating in an inertia running state, e.g., where the bicycle is operated in a state in which the bicycle is not driven through rotation of the gear crank (corresponding to the crankshaft) in its normal rotating direction. In this state, positioning the chain among a plurality of small gears cannot perform power transmission.
Although the chain wound around the one large gear is positioned among a plurality of small gears arranged in a direction of the rotating central line for transmission, when the chain is applied between the large gear and the small gears placed at different positions in the rotating central line direction of the large gear (or small gears), it is sometimes found that the chain becomes offset with respect to a plane crossing at a right angle with the rotating central line. Accordingly, the chain can be removed from either the large gear or the small gears. Then, when a distance between the large gear and the small gears is relatively small, the inclination of the chain in respect to the crossing plane becomes excessively large, and the chain can be easily removed or dislodged from the gears.
In addition, when the bicycle is in an inertial operating state, a tension force of the chain is at a relative low value. Therefore, when the chain is inclined with respect to the crossing plane, the chain is in a such state in which it can be dislodged from either the large gear or the small gears more easily than compared with an operating state in which the crankshaft is being rotated in its normal rotational direction.